-- BELOW IS A SAMPLE WHICH OUTLINES THE SIMPLE DIFFERENCES
-- READ IT AND THEN EXECUTE IT
-- THERE ARE THREE ROWS OF EACH COLOR INSERTED INTO THE TABLE
-- CREATE A database called testDB


-- use testDB
USE [TestDB]
GO


-- create Paints table
CREATE TABLE [dbo].[Paints](
    [Color] [varchar](50) NULL,
    [glossLevel] [varchar](50) NULL
) ON [PRIMARY]

GO


-- Populate Table
insert into paints (color, glossLevel)
select 'red', 'eggshell'
union
select 'red', 'glossy'
union
select 'red', 'flat'
union
select 'blue', 'eggshell'
union
select 'blue', 'glossy'
union
select 'blue', 'flat'
union
select 'orange', 'glossy'
union
select 'orange', 'flat'
union
select 'orange', 'eggshell'
union
select 'green', 'eggshell'
union
select 'green', 'glossy'
union
select 'green', 'flat'
union
select 'black', 'eggshell'
union
select 'black', 'glossy'
union
select 'black', 'flat'
union
select 'purple', 'eggshell'
union
select 'purple', 'glossy'
union
select 'purple', 'flat'
union
select 'salmon', 'eggshell'
union
select 'salmon', 'glossy'
union
select 'salmon', 'flat'


/*   COMPARE 'GROUP BY' color to 'OVER (PARTITION BY Color)'  */

-- GROUP BY Color 
-- row quantity defined by group by
-- aggregate (count(*)) defined by group by
select count(*) from paints
group by color

-- OVER (PARTITION BY... Color 
-- row quantity defined by main query
-- aggregate defined by OVER-PARTITION BY
select color
, glossLevel
, count(*) OVER (Partition by color)
from paints

/* COMPARE 'GROUP BY' color, glossLevel to 'OVER (PARTITION BY Color, GlossLevel)'  */

-- GROUP BY Color, GlossLevel
-- row quantity defined by GROUP BY
-- aggregate (count(*)) defined by GROUP BY
select count(*) from paints
group by color, glossLevel



-- Partition by Color, GlossLevel
-- row quantity defined by main query
-- aggregate (count(*)) defined by OVER-PARTITION BY
select color
, glossLevel
, count(*) OVER (Partition by color, glossLevel)
from paints

PARTITION BY是分析的，GROUP BY是聚合的。为了使用PARTITION BY，你必须用OVER子句来包含它。

假设我们在表中有14条name列的记录

在小组由

select name,count(*) as totalcount from person where name='Please fill out' group BY name;

它将给出单行计数，即14

但是在除以

select row_number() over (partition by name) as total from person where name = 'Please fill out';

它将增加14行计数

它提供汇总数据而不进行汇总

例如，假设我想返回销售区域的相对位置

使用PARTITION BY，我可以返回给定区域的销售额和同一行中所有销售区域的最大销售额。

这确实意味着您将有重复的数据，但它可能适合最终消费者，因为数据已经聚合，但没有数据丢失——就像GROUP BY的情况一样。

它有非常不同的使用场景。 当您使用GROUP BY时，您合并了相同列的一些记录，并获得了结果集的聚合。

然而，当你使用PARTITION BY时，你的结果集是相同的，但你只是对窗口函数进行了聚合，而你没有合并记录，你仍然会有相同的记录计数。

以下是一篇对市场有帮助的文章，解释了两者的区别: http://alevryustemov.com/sql/sql-partition-by/

小的观察。使用“partition by”动态生成SQL的自动化机制相对于“group by”要简单得多。对于“group by”，我们必须注意“select”列的内容。

对不起，我的英语不好。